Migration of Integer to inline

[Brian Goetz]

> If non-Object abstract class as superclass of inline class is allowed, the
> migration story for Optional seems easy.
> It would be the same for Integer, if only there were no pesky public
> Integer::new...

These constructors have been deprecated since Java 9; and there has been 
IDE support for migrating invocations of these to the appropriate 
factory methods for at least a dozen years.  It is reasonable to 
deprecate them for removal.

As with `new Object()`, it is also possible to take heroic measures to 
relink `new Ljava/lang/Integer;` bytecodes to instantiate some other 
type, though we're not ready to plunk for that yet (it's more 
complicated than for Object.)

Bytecode weaving (perhaps even at load time, with an agent) is indeed a 
possible means of rewriting these dusty jars.

>
> Could you share any preliminary thoughts how the classfiles (found in
> *dusty* jars) that use the Integer constructor would be treated?
>
> Is it feasible to have the bytecode weaved to replace the new-dup-init
> sequence during class loading?
>
> Thanks,
> Mateusz